Re: [PATCH] x86_64: sync_tsc fix the race (so we can boot)

[yhlu <yhlu.kernel@gmail.com>]

Do you mean solve the timing problem for 2 way dual core or 4 way
single core above?

YH

On 7/27/05, Eric W. Biederman <ebiederm@xmission.com> wrote:
> 
> sync_tsc was using smp_call_function to ask the boot processor
> to report it's tsc value.  smp_call_function performs an IPI_send_allbutself
> which is a broadcast ipi.  There is a window during processor startup during
> which the target cpu has started and before it has initialized it's interrupt
> vectors so it can properly process an interrupt.  Receveing an interrupt
> during that window will triple fault the cpu and do other nasty things.
> 
> Why cli does not protect us from that is beyond me.
> 
> The simple fix is to match ia64 and provide a smp_call_function_single.
> Which avoids the broadcast and is more efficient.
> 
> This certainly fixes the problem of getting stuck on boot which was
> very easy to trigger on my SMP Hyperthreaded Xeon, and I think
> it fixes it for the right reasons.
> 
> I believe this patch suffers from apicid versus logical cpu number confusion.
> I copied the basic logic from smp_send_reschedule and I can't find where
> that translates from the logical cpuid to apicid.  So it isn't quite
> correct yet.  It should be close enough that it shouldn't be too hard
> to finish it up.
> 
> More bug fixes after I have slept but I figured I needed to get this
> one out for review.
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> 
> ---
> 
>  arch/x86_64/kernel/smp.c     |   65 ++++++++++++++++++++++++++++++++++++++++++
>  arch/x86_64/kernel/smpboot.c |   21 ++++++++------
>  include/asm-x86_64/smp.h     |    2 +
>  3 files changed, 79 insertions(+), 9 deletions(-)
> 
> 571d8bdc5a935b85fb0ce5ff3fac9a59a86efe6e
> diff --git a/arch/x86_64/kernel/smp.c b/arch/x86_64/kernel/smp.c
> --- a/arch/x86_64/kernel/smp.c
> +++ b/arch/x86_64/kernel/smp.c
> @@ -294,6 +294,71 @@ void unlock_ipi_call_lock(void)
>  }
> 
>  /*
> + * this function sends a 'generic call function' IPI to one other CPU
> + * in the system.
> + */
> +static void __smp_call_function_single (int cpu, void (*func) (void *info), void *info,
> +                               int nonatomic, int wait)
> +{
> +       struct call_data_struct data;
> +       int cpus = 1;
> +
> +       data.func = func;
> +       data.info = info;
> +       atomic_set(&data.started, 0);
> +       data.wait = wait;
> +       if (wait)
> +               atomic_set(&data.finished, 0);
> +
> +       call_data = &data;
> +       wmb();
> +       /* Send a message to all other CPUs and wait for them to respond */
> +       send_IPI_mask(cpumask_of_cpu(cpu), CALL_FUNCTION_VECTOR);
> +
> +       /* Wait for response */
> +       while (atomic_read(&data.started) != cpus)
> +               cpu_relax();
> +
> +       if (!wait)
> +               return;
> +
> +       while (atomic_read(&data.finished) != cpus)
> +               cpu_relax();
> +}
> +
> +/*
> + * Run a function on another CPU
> + *  <func>     The function to run. This must be fast and non-blocking.
> + *  <info>     An arbitrary pointer to pass to the function.
> + *  <nonatomic>        Currently unused.
> + *  <wait>     If true, wait until function has completed on other CPUs.
> + *  [RETURNS]   0 on success, else a negative status code.
> + *
> + * Does not return until the remote CPU is nearly ready to execute <func>
> + * or is or has executed.
> + */
> +
> +int smp_call_function_single (int cpu, void (*func) (void *info), void *info,
> +       int nonatomic, int wait)
> +{
> +
> +       int me = get_cpu(); /* prevent preemption and reschedule on another processor */
> +
> +       if (cpu == me) {
> +               printk("%s: trying to call self\n", __func__);
> +               put_cpu();
> +               return -EBUSY;
> +       }
> +       spin_lock_bh(&call_lock);
> +
> +       __smp_call_function_single(cpu, func,info,nonatomic,wait);
> +
> +       spin_unlock_bh(&call_lock);
> +       put_cpu();
> +       return 0;
> +}
> +
> +/*
>   * this function sends a 'generic call function' IPI to all other CPUs
>   * in the system.
>   */
> diff --git a/arch/x86_64/kernel/smpboot.c b/arch/x86_64/kernel/smpboot.c
> --- a/arch/x86_64/kernel/smpboot.c
> +++ b/arch/x86_64/kernel/smpboot.c
> @@ -229,9 +229,6 @@ static __cpuinit void sync_master(void *
>  {
>         unsigned long flags, i;
> 
> -       if (smp_processor_id() != boot_cpu_id)
> -               return;
> -
>         go[MASTER] = 0;
> 
>         local_irq_save(flags);
> @@ -280,7 +277,7 @@ get_delta(long *rt, long *master)
>         return tcenter - best_tm;
>  }
> 
> -static __cpuinit void sync_tsc(void)
> +static __cpuinit void sync_tsc(unsigned int master)
>  {
>         int i, done = 0;
>         long delta, adj, adjust_latency = 0;
> @@ -294,9 +291,17 @@ static __cpuinit void sync_tsc(void)
>         } t[NUM_ROUNDS] __cpuinitdata;
>  #endif
> 
> +       printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n",
> +               smp_processor_id(), master);
> +
>         go[MASTER] = 1;
> 
> -       smp_call_function(sync_master, NULL, 1, 0);
> +       /* It is dangerous to broadcast IPI as cpus are coming up,
> +        * as they may not be ready to accept them.  So since
> +        * we only need to send the ipi to the boot cpu direct
> +        * the message, and avoid the race.
> +        */
> +       smp_call_function_single(master, sync_master, NULL, 1, 0);
> 
>         while (go[MASTER])      /* wait for master to be ready */
>                 no_cpu_relax();
> @@ -340,16 +345,14 @@ static __cpuinit void sync_tsc(void)
>         printk(KERN_INFO
>                "CPU %d: synchronized TSC with CPU %u (last diff %ld cycles, "
>                "maxerr %lu cycles)\n",
> -              smp_processor_id(), boot_cpu_id, delta, rt);
> +              smp_processor_id(), master, delta, rt);
>  }
> 
>  static void __cpuinit tsc_sync_wait(void)
>  {
>         if (notscsync || !cpu_has_tsc)
>                 return;
> -       printk(KERN_INFO "CPU %d: Syncing TSC to CPU %u.\n", smp_processor_id(),
> -                       boot_cpu_id);
> -       sync_tsc();
> +       sync_tsc(boot_cpu_id);
>  }
> 
>  static __init int notscsync_setup(char *s)
> diff --git a/include/asm-x86_64/smp.h b/include/asm-x86_64/smp.h
> --- a/include/asm-x86_64/smp.h
> +++ b/include/asm-x86_64/smp.h
> @@ -48,6 +48,8 @@ extern void unlock_ipi_call_lock(void);
>  extern int smp_num_siblings;
>  extern void smp_flush_tlb(void);
>  extern void smp_message_irq(int cpl, void *dev_id, struct pt_regs *regs);
> +extern int smp_call_function_single (int cpuid, void (*func) (void *info), void *info,
> +                                    int retry, int wait);
>  extern void smp_send_reschedule(int cpu);
>  extern void smp_invalidate_rcv(void);          /* Process an NMI */
>  extern void zap_low_mappings(void);
> -
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